Hello Avri,
On 26/09/23 11:54, Avri Altman wrote:
With fortify enabled gcc throws following error:
from mmc_cmds.c:20:
In function ‘read’,
inlined from ‘do_rpmb_write_key’ at mmc_cmds.c:2233:8:
/home/giuliobenetti/br_reproduce/a53922c5db3e605a5e81e53c034f45017e
bb7db7/output/host/mipsel-buildroot-linux-
gnu/sysroot/usr/include/bits/unistd.h:38:10: error: ‘__read_alias’ writing
228 or more bytes into a region of size 32 overflows the destination [-
Werror=stringop-overflow=]
38 | return __glibc_fortify (read, __nbytes, sizeof (char),
| ^~~~~~~~~~~~~~~
mmc_cmds.c: In function ‘do_rpmb_write_key’:
mmc_cmds.c:2087:19: note: destination object ‘key_mac’ of size 32
2087 | u_int8_t key_mac[32];
| ^~~~~~~
/home/giuliobenetti/br_reproduce/a53922c5db3e605a5e81e53c034f45017e
bb7db7/output/host/mipsel-buildroot-linux-
gnu/sysroot/usr/include/bits/unistd.h:26:16: note: in a call to function
‘__read_alias’ declared with attribute ‘access (write_only, 2, 3)’
26 | extern ssize_t __REDIRECT (__read_alias, (int __fd, void *__buf,
| ^~~~~~~~~~
read() could potentially return more than nbyte so let's check for ret < nbyte.
No it can't because that would mean buffer overflow.
See https://pubs.opengroup.org/onlinepubs/9699919799/functions/read.html :
" this number shall never be greater than nbyte."
So this seems like a bogus warning to me.
Yes, you're right, and after doing some test this error appear with
_FORTIFY_SOURCE=3 but it doesn't with _FORTIFY_SOURCE=2 or 1.
So yes. I'm going to reword like:
```
Building with _FORTIFY_SOURCE=3 results in:
from mmc_cmds.c:20:
In function ‘read’,
inlined from ‘do_rpmb_write_key’ at mmc_cmds.c:2233:8:
/home/giuliobenetti/br_reproduce/a53922c5db3e605a5e81e53c034f45017e
bb7db7/output/host/mipsel-buildroot-linux-
gnu/sysroot/usr/include/bits/unistd.h:38:10: error: ‘__read_alias’ writing
228 or more bytes into a region of size 32 overflows the destination [-
Werror=stringop-overflow=]
38 | return __glibc_fortify (read, __nbytes, sizeof (char),
| ^~~~~~~~~~~~~~~
mmc_cmds.c: In function ‘do_rpmb_write_key’:
mmc_cmds.c:2087:19: note: destination object ‘key_mac’ of size 32
2087 | u_int8_t key_mac[32];
| ^~~~~~~
/home/giuliobenetti/br_reproduce/a53922c5db3e605a5e81e53c034f45017e
bb7db7/output/host/mipsel-buildroot-linux-
gnu/sysroot/usr/include/bits/unistd.h:26:16: note: in a call to function
‘__read_alias’ declared with attribute ‘access (write_only, 2, 3)’
26 | extern ssize_t __REDIRECT (__read_alias, (int __fd, void *__buf,
| ^~~~~~~~~~
To work around this let's check if the return of read() is lower than
the nbyte requested instead of not equal.
```
Does it look good for you?
Best regards
--
Giulio Benetti
CEO&CTO@Benetti Engineering sas
Thanks,
Avri
Signed-off-by: Giulio Benetti <giulio.benetti@xxxxxxxxxxxxxxxxxxxxxx>
---
mmc_cmds.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mmc_cmds.c b/mmc_cmds.c
index 10d063d..ae7b876 100644
--- a/mmc_cmds.c
+++ b/mmc_cmds.c
@@ -2065,7 +2065,7 @@ int do_sanitize(int nargs, char **argv)
} \
else if (r > 0) \
ret += r; \
- } while (r != 0 && (size_t)ret != nbyte); \
+ } while (r != 0 && (size_t)ret < nbyte); \
\
ret; \
})
--
2.34.1
